As the administration dismantles its only backup system, the Air Force looks at replacements to guard against the Pentagon's over-reliance on GPS satellites.

Last week, the Air Force's Chief of Staff, Gen. Norton Schwartz, gave voice to a chink in the U.S. military's armor, one that many know about but few like to discuss in public: Without satellites, modern militaries lose most of their edge. "It seemed critical to me that the joint force reduce its dependence on GPS (Global Positioning System)," he told attendees at a national security conference in Washington.

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There are two main reasons why a GPS system might fail: spoofing and jamming. Spoofing can trick the GPS system into showing a false location. This is especially dangerous with bombs, unmanned aircraft and missiles that use GPS for guidance. Enemies on the ground can also jam signals from the satellite, while more technologically-advanced foes can fire kamikaze space vehicles that could disable a satellite at a critical moment. Schwartz assured the audience that Air Force researchers are busy designing backups to GPS.

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"The Air Force wants a system that will still be up when, or if, the current system is attacked in some way," says Leemon Baird, a senior research scientist at the Academy Center for Cyber Space Research (ACCSR). "If you have multiple systems it is harder to attack them all."

The Obama administration is also moving forward on a plan to shut down the only current backup to GPS, a permanent ground station network called LORAN-C that is run by the Coast Guard. The Department of Homeland Security last year started a painful upgrade to LORAN-C, adding modern electronics and solid-state transmitters, despite the fact that in 2008 President George W. Bush signed a law that scheduled the system's dissolution.

The improved system, called eLORAN, would acquire loctaions by triangulating signals from ground stations and be able to pass detailed information through an improved communication channel. The new hardware would also have a data channel that could handle more detailed information. But LORAN-C—the only functioning backup to GPS—will be dismantled by October 2010, according to an early January Coast Guard announcement in the Federal Register. With LORAN-C dead, the upgraded system is now useless.

The Air Force is now researching ways to install navigation equipment closer to Earth than orbiting satellites. Aircraft, blimps and temporary ground stations can be used to provide navigation beacons. Researchers call these "pseudolites" for psuedo satellites. The Air Force is also looking at new technology to serve as a backup, including inertial navigation systems that have sensors that track movement and use that data to plot a position. When combined with laser radar, which flickers across the terrain to recognize familiar landmarks, these systems can guide aircraft or missiles to the right place. Unmanned aerial vehicles have inertial navigation backup systems in case they lose contact with ground controllers.

In the days before GPS, fliers and ground troops used more than technology to figure out where they were, and their old-school techniques are still reliable. Pilots, for example, can use dead reckoning to find their way. "They can look at your air speed and say, 'I've been flying this fast for this long and my compass says I am going in this direction,'" says Baird. In a similar way, a ground control station flying an unmanned aerial vehicle could plot the same data and get their misplaced aircraft where it needs to be.